Photochromic polyurethane laminate

Abstract

A photochromic polyurethane laminate that is constructed to solve certain manufacturing difficulties involved in the production of plastic photochromic lenses is disclosed. The photochromic laminate includes at least two layers of a resinous material and a photochromic polyurethane layer that is interspersed between the two resinous layers and which contains photochromic compounds. The polyurethane layer is formed by curing a mixture of a solid thermoplastic polyurethane, at least one isocyanate prepolymer, at least one photochromic compound, and a stabilizing system.

Claims

1. A photochromic polyurethane layer prepared from a mixture comprising a polyurethane, an isocyanate-terminated polyurethane prepolymer, and a photochromic compound; the polyurethane having a number average molecular weight from 9,000 to 100,000 and prepared from a composition comprising: an aliphatic diisocyanate comprising 4,4′-dicyclohexylmethanediiso-cyanate; a polyester polyol; and a chain extender; the isocyanate-terminated polyurethane prepolymer prepared from a composition comprising: an aliphatic diisocyanate comprising 4,4′-dicyclohexylmethanediiso-cyanate; and a polyester polyol; wherein a mixing ratio of the polyurethane and the isocyanate-terminated polyurethane prepolymer by weight is in a range from 1:9 to 9:1 and said polyurethane comprises terminal hydroxyl groups, urethane groups and urea groups having active hydrogen atoms to react with said isocyanate-terminated polyurethane prepolymer after lamination to provide further curability of said photochromic polyurethane layer.

2. The photochromic polyurethane layer of claim 1 wherein the polyurethane and the isocyanate-terminated polyurethane prepolymer are prepared from the same aliphatic diisocyanate.

3. The photochromic polyurethane layer of claim 1 wherein the polyurethane and the isocyanate-terminated polyurethane prepolymer are prepared from the same polyester polyol.

4. The photochromic polyurethane layer of claim 1 wherein the polyurethane and the isocyanate-terminated polyurethane prepolymer are prepared from different polyester polyols.

5. The photochromic polyurethane layer of claim 1 wherein the polyurethane is prepared from a composition comprising a polycaprolactone.

6. The photochromic polyurethane layer of claim 1 wherein the polyurethane is prepared from a composition comprising a polycaprolactone having a number average molecular weight of about 1000 grams per mole.

7. The photochromic polyurethane layer of claim 1 wherein the polyurethane is prepared from a composition comprising a diol as a chain extender having a molecular weight in the range of approximately 62 to 499 grams per mole.

8. The photochromic polyurethane layer of claim 1 wherein the polyurethane is prepared from a composition comprising 1,4-butane-diol as the chain extender.

9. The photochromic polyurethane layer of claim 1 wherein the isocyanate-terminated polyurethane prepolymer is prepared from a composition comprising a polycaprolactone.

10. The photochromic polyurethane layer of claim 1 wherein the isocyanate-terminated polyurethane prepolymer is prepared from a composition comprising a polycaprolactone having a number average molecular weight of about 1000 grams per mole.

11. The photochromic polyurethane layer of claim 1 wherein the polyester polyol has an OH number of 112 milligrams KOH per gram to prepare said polyurethane and said isocyanate-terminated polyurethane prepolymer.

12. The photochromic polyurethane layer of claim 1 wherein the photochromic compound is selected from a group consisting of: benzopyrans, naphthopyrans, spirobenzopyrans, spironaphthopyrans, spirobenzoxzines, spironaph-thoxazines, fulgides and fulgim ides.

13. A photochromic laminate for use in eyeglasses comprising: a first resin sheet; a second resin sheet; a photochromic polyurethane film having a first side bonded to the first resin sheet and a second side bonded to the second resin sheet; the photochromic polyurethane film prepared from a composition comprising: a polyurethane having a number average molecular weight from 9,000 to 100,000 and prepared from a composition comprising: an aliphatic diisocyanate comprising 4,4′-dicyclohexylmethane-diisocyanate; a polyester polyol; and a chain extender; an isocyanate-terminated polyurethane prepolymer prepared from a composition comprising: an aliphatic diisocyanate comprising 4,4′-dicyclohexylmethanediiso-cyanate; and a polyester polyol; and a photochromic compound; wherein a mixing ratio of the polyurethane and the isocyanate-terminated polyurethane prepolymer by weight is in a range from 1:9 to 9:1 and said polyurethane comprises terminal hydroxyl groups, urethane groups, and urea groups having active hydrogen atoms to react with said polyurethane prepolymer after lamination to provide further curability of said photochromic polyurethane film between the first resin sheet and the second resin sheet.

14. The photochromic laminate of claim 13 wherein the first resin sheet and the second resin sheet comprise polycarbonate.

15. The photochromic laminate of claim 13 wherein the polyurethane and the isocyanate-terminated polyurethane prepolymer are prepared from the same polyester polyol.

16. The photochromic laminate of claim 13 wherein the polyurethane is prepared from a composition comprising a polycaprolactone having a number average molecular weight of about 1000 grams per mole.

17. The photochromic laminate of claim 13 wherein the photochromic compound is selected from a group consisting of: benzopyrans, naphthopyrans, spirobenzopyrans, spironaphthopyrans, spirobenzoxzines, spironaph-thoxazines, fulgides and fulgim ides.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The present invention provides a photochromic polyurethane laminate having two transparent resin sheets bonded to a photochromic polyurethane layer formed by curing a mixture of a solid thermoplastic polyurethane, at least one isocyanate prepolymer, at least one photochromic compound, and a stabilizing system. The thermoplastic polyurethane has a theoretical NCO index of from 90 to 105, and a molecular weight (number averaged) of from 20,000 to 100,000. The isocyanate prepolymer has a NCO content of from 1.0% to 10.0%, by weight. The weight ratio of the thermoplastic polyurethane vs. the isocyanate prepolymer in the photochromic polyurethane composition is in the range from 1:9 to 9:1. The photochromic compound(s) counts for 0.1% to 5% of the total polyurethane, by weight.

(2) To enhance the fatigue resistance of the photochromic compounds, stabilizers such as antioxidants, light stabilizers, and UV absorbers are added in the polyurethane layer.

(3) The photochromic laminate is preferably made through a cast-lamination process. All components described above are dissolved in a suitable solvent, cast on a release liner. After the solvent is evaporated substantially, the thermoplastic polyurethane portion will provide the cast polyurethane film enough rigidity to go through the lamination process without any deformation. After lamination, the polyurethane prepolymer will provide further curability by reacting with active hydrogen atoms such as those of terminal hydroxyl groups, moisture, urethane groups, and urea groups in the system to enhance the dimensional stability of the polyurethane layer under high temperature and high pressure.

(4) Transparent Resin Sheets

(5) The material used to make the transparent resin sheet is not limited so long as it is a resin with high transparency. In case the photochromic polyurethane laminate of the present invention is incorporated into a thermoplastic article such as a spectacle lens, the transparent resin sheets of the laminate is preferably of a resin material that is thermally fusible to the article base material so that the photochromic laminate is tightly integrated with the article base when produced with the insert injection molding process. Thus, it is more preferred to have same kind of material for both the article base and the transparent resin sheets.

(6) Suitable sheet resin materials include polycarbonate, polysulfone, cellulose acetate butyrate (CAB), polyacrylates, polyesters, polystyrene, copolymer of an acrylate and styrene, blends of compatible transparent polymers. Preferred resins are polycarbonate, CAB, polyacrylates, and copolymers of acrylate and styrene. A polycarbonate-based resin is particularly preferred because of high transparency, high tenacity, high thermal resistance, high refractive index, and most importantly, and especially its compatibility with the article base material when polycarbonate photochromic lenses are manufactured with the photochromic polyurethane laminate of the present invention and the insert injection molding process. A typical polycarbonate based resin is polybisphenol-A carbonate. In addition, examples of the polycarbonate based resin include homopolycarbonate such as 1,1′-dihydroxydiphenyl-phenylmethylmethane, 1,1′-dihydroxydiphenyl-diphenylmethane, 1,1′-dihydroxy-3,3′-dimethyldiphe-nyl-2,2-propane, their mutual copolymer polycarbonate and copolymer polycarbonate with bisphenol-A.

(7) While the thickness of a transparent resin sheet is not particularly restricted, it is typically 2 mm or less, and preferably 1 mm or less but not less than 0.025 mm.

(8) Thermoplastic Polyurethane

(9) As the thermoplastic polyurethane, it is preferably made from a diisocyanate, a polyol, and a chain extender. Thermoplastic polyurethanes of this kind are known and may be obtained, for example, in accordance with U.S. Pat. Nos. 3,963,679 and 4,035,213, the disclosures of which are incorporated herein by reference.

(10) The thermoplastic polyurethane used in the present invention is particularly prepared from a composition comprising a) an aliphatic isocyanate having a functionality of 2, b) at least one high molecular weight polyol having a nominal functionality of 2 and a molecular weight of from 500 to 6000 g/mole, preferably from 700 to 3000 g/mol, and counting for from about 50% to about 98% by weight, preferably from 70% to 95%, of the total isocyanate reactive species in the composition, and c) at least one low molecular weight diol having a molecular weight of from 62 to 499, and counting for from about 2% to about 50% by weight, preferably from 5% to 30%, of the total isocyanate reactive species in the composition.

(11) Polyols

(12) The polyols of the present invention are those conventionally employed in the art for the preparation of polyurethane cast elastomers. Naturally, and often times advantageously, mixtures of such polyols are also possible. Examples of the suitable polyols include polyether polyols, polyester polyols, polyurethane polyols, polybutadiene polyol, and polycarbonate polyols, while polyether and polyester types are preferred.

(13) Included among suitable polyether polyols are polyoxyethylene glycol, polyoxypropylene glycol, polyoxybutylene glycol, polytetramethylene glycol, block copolymers, for example, combinations of polyoxypropylene and polyoxyethylene glycols, poly-1,2-oxybutylene and polyoxyethylene glycols, poly-1,4-tetramethylene and polyoxyethylene glycols, and copolymer glycols prepared from blends or sequential addition of two or more alkylene oxides. The polyalkylene polyether polyols may be prepared by any known process such as, for example, the process disclosed in Encyclopedia of Chemical Technology, Vol. 7, pp. 257-262, published by Interscience Publishers, Inc. (1951), the disclosure of which is incorporated herein by reference.

(14) Polyethers which are preferred include the alkylene oxide addition products of polyhydric alcohols such as ethylene glycol, propylene glycol, dipropylene glycol, trimethylene glycol, 1,2-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, hydroquinone, resorcinol glycerol, glycerine, 1,1,1-trimethylol-propane, 1,1,1-trimethylolethane, pentaerythritol, 1,2,6-hexanetriol, .alpha.-methyl glucoside, sucrose, and sorbitol. Also included within the term “polyhydric alcohol” are compounds derived from phenol such as 2,2-bis (4-hydroxyphenyl)-propane, commonly known as Bisphenol A.

(15) The suitable polyester polyols include the ones which are prepared by polymerizing ε-caprolactone using an initiator such as ethylene glycol, ethanolamine and the like. Further suitable examples are those prepared by esterification of polycarboxylic acids. Further suitable polyester polyols include reaction products of polyhydric, preferably dihydric alcohols to which trihydric alcohols may be added and polybasic, preferably dibasic carboxylic acids. Instead of these polycarboxylic acids, the corresponding carboxylic acid anhydrides or polycarboxylic acid esters of lower alcohols or mixtures thereof may be used for preparing the polyesters. The polycarboxylic acids may be aliphatic, cycloaliphatic, aromatic and/or heterocyclic and they may be substituted, e.g., by halogen atoms, and/or unsaturated. The following are mentioned as examples: succinic acid; adipic acid; suberic acid; azelaic acid; sebacic acid; phthalic acid; isophthalic acid; trimellitic acid; phthalic acid anhydride; tetrahydrophthalic acid anhydride; hexahydrophthalic acid anhydride; tetrachlorophthalic acid anhydride, endomethylene tetrahydrophthalic acid anhydride; glutaric acid anhydride; maleic acid; maleic acid anhydride; fumaric acid; dimeric and trimeric fatty acids such as oleic acid, which may be mixed with monomeric fatty acids; dimethyl terephthalates and bis-glycol terephthalate. Suitable polyhydric alcohols include, e.g., ethylene glycol; propylene glycol-(1,2) and -(1,3); butylene glycol-(1,4) and -(1,3); hexanediol-(1,6); octanediol-(1,8); neopentyl glycol; (1,4-bis-hydroxymethylcyclohexane); 2-methyl-1,3-propanediol; 2,2,4-trimethyl-1,3-pentanediol; triethylene glycol; tetraethylene glycol; polyethylene glycol; dipropylene glycol; polypropylene glycol; dibutylene glycol and polybutylene glycol, glycerine and trimethlyolpropane. A preferred polyester polyol is polycaprolactone polyol having an average molecular weight from 500 to 6,000, and preferably from 700 to 3,000.

(16) Diols

(17) Suitable diols are those polyols listed above having a functionality of 2 and a molecular weight of from 62 to 499. Preferred diols are 1,4-butane-diol and 1,3-propane-diol.

(18) Isocyanates

(19) The diisocyanate component is preferably an aliphatic diisocyanate. The aliphatic diisocyanate is selected from the group consisting of 1,4-tetramethylene diisocyanate, 1,6-hexamethylene diisocyanate, 2,2,4-trimethyl-1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, cyclohexane-1,3- and -1,4-diisocyanate, 1-isocyanato-2-isocyanatomethyl cyclopentane, 1-isocyanato-3-isocyanatomethyl-3,5,5-trimethyl-cyclohexane (isophorone diisocyanate or IPDI), bis-(4-isocyanatocyclohexyl)-methane, 2,4′-dicyclohexylmethane diisocyanate, 1,3- and 1,4-bis-(isocyanatomethyl)-cyclohexane, bis-(4-isocyanato-3-methylcyclohexyl)-methane, .alpha.,.alpha.,.alpha.′,.alpha.′-tetramethyl-1,3- and/or -1,4-xylylene diisocyanate, 1-isocyanato-1-methyl-4(3)-isocyanatomethyl cyclohexane, 2,4- and/or 2,6-hexahydrotoluylene diisocyanate, and mixtures thereof. Bis-(4-isocyanatocyclohexl)-methane is the preferred diisocyanate in occurrence with the method of the present invention.

(20) The polymerization process to make the thermoplastic polyurethane can be carried out in one-pot fashion, that is, all starting materials are initially added into the reaction vessel. The polymerization process can also be carried out with a prepolymer approach. That is, a polyurethane prepolymer terminated with isocyanate groups is first obtained by reacting a stoichiometrically in excess diisocyanate with a polyol. Suitable equivalent ratio of diisocyanate to polyol in the present invention is from 1.2:1.0 to 8.0:1.0. A chain extender of diol is then mixed with the prepolymer to complete the reaction. The NCO index of the thermoplastic polyurethane, formed from the quotient, which is multiplied by 100, of the equivalent ratio of isocyanate groups to the sum of the hydroxyl groups of polyol and chain extender is within a range of 90 to 105, preferably between 92 and 101.

(21) Catalysts such as organotin or other metallic soaps may be added in the mixture to make a thermoplastic polyurethane. Example catalysts include dibutyltin dilaurate, stannous octoate, and cobalt naphthenate.

(22) Isocyanate Prepolymer

(23) The isocyanate prepolymer used in the photochromic polyurethane composition of the present invention is prepared in the same way as the prepolymer used to prepare the thermoplastic polyurethane in a prepolymer method described above. Preferably, the polyol and the isocyanate used to make the isocyanate prepolymer is the same as the polyol to make the thermoplastic polyurethane. More preferably, the isocyanate is an aliphatic diisocyanate described in the previous sections, and the polyol is a polyester polyol having a molecular weight between 700 and 3,000. The molecular weight (number averaged) of the isocyanate prepolymer is preferably between 1,000 and 6,000, and more preferably between 1,500 and 4,000. As an isocyanate group terminated prepolymer, its NCO content is between 1.0% and 10.0%, preferably between 2.0% and 8.0%.

(24) When mixing the isocyanate prepolymer and the thermoplastic polyurethane together, the mixing ratio by weight is in the range from 1:9 to 9:1, preferably from 1:3 to 3:1.

(25) Photochromic Compounds

(26) Suitable photochromic compounds in the context of the invention are organic compounds that, in solution state, are activated (darken) when exposed to a certain light energy (e.g., outdoor sunlight), and bleach to clear when the light energy is removed. They are selected from the group consisting essentially of benzopyrans, naphthopyrans, spirobenzopyrans, spironaphthopyrans, spirobenzoxzines, spironaphthoxazines, fulgides and fulgim ides. Such photochromic compounds have been reported which, for example, in U.S. Pat. Nos. 5,658,502, 5,702,645, 5,840,926, 6,096,246, 6,113,812, and 6,296,785; and U.S. patent application Ser. No. 10/038,350, all commonly assigned to the same assignee as the present invention and all incorporated herein by reference.

(27) Among the photochromic compounds identified, naphthopyran derivatives are preferred for optical articles such as eyewear lenses. They exhibit good quantum efficiency for coloring, a good sensitivity and saturated optical density, an acceptable bleach or fade rate, and most importantly good fatigue behavior. These compounds are available to cover the visible light spectrum from 400 nm to 700 nm. Thus, it is possible to obtain a desired blended color, such as neutral gray or brown, by mixing two or more photochromic compounds having complementary colors under an activated state.

(28) More preferred are naphtho[2,1b]pyrans and naphtho[1,2b]pyrans represented by the following generic formula:

(29) ##STR00001##

(30) Substituents on various positions of the aromatic structure are used to tune the compounds to have desired color and fading rate, and improved fatigue behavior. For example, a photochromic dye may contain a polymerizable group such as a (meth)acryloyloxy group or a (meth)allyl group, so that it can be chemically bonded to the host material through polymerization.

(31) The quantity of photochromic compound(s) incorporated into the polyurethane layer of the present invention is determined by the desired light blockage in the activated state and the thickness of the polyurethane layer itself. The preferred outdoor visible light transmission of sunglasses is preferably between 5% and 50%, more preferably between 8% and 30%, most preferably between 10% and 20%. Preferably, the amount of total photochromic substance incorporated into or applied on the polyurethane layer may range from about 0.1 wt. % to about 5 wt. % of the total polyurethane, and more preferably from about 0.5 wt. % to about 3.0 wt. %. If the thickness of the polyurethane layer is 100 μm, between about 0.5 wt. % to about 1 wt. % of photochromic compound(s) is needed to achieve an outdoor light transmission of between 10% and 20%. The amount of photochromic compound(s) needed is inversely proportional to the thickness of the polyurethane layer. In other words, to achieve the same outdoor light transmission the thicker the polyurethane layer, the lower the concentration of photochromic compound(s) needed. The concentration of the photochromic compound(s) also depends on the color intensity of the photochromic compound(s) at the activated state.

(32) Stabilizers

(33) Additives such as antioxidants and light stabilizers are incorporated into the polyurethane layer in order to improve the fatigue resistance of the photochromic compounds. Hindered amines are usually used as light stabilizers, and hindered phenols are usually used as antioxidants. Preferred hindered amine light stabilizers include, bis(1,2,2,6,6-pentamethyl-4-piperidinyl)-sebacate, or a condensation product of 1,2,2,6,6-pentamethyl-4-piperidinol, tridodecyl alcohol and 1,2,3,4-butanetetra caboxylic acid as tertiary hindered amine compounds. Preferred phenol antioxidants include, 1,1,3-tris(2-methyl-4-hydorxy-5-t-butylphenyl)butane, tetrakis-[methylene-3-(3′,5′-di-t-butyl-4′-hydroxy-phenyl)propionate]methane, and 1,3,5-tris(3,5-di-t-butyl-4-hyroxybenzyl)-1,-3,5-triazine-2,4,6-(1H,3H,5H)-trione. Phenol antioxidants that contain 3 or more hindered phenols are preferable.

(34) Process to Make the Laminate

(35) A photochromic laminate having a polyurethane layer in between two transparent resin sheets in accordance with the present invention may be produced through a variety of processes. Depending on the nature of the starting material to the polyurethane, processes such as casting-lamination (also referred to in the art as coating-lamination), and extrusion-lamination may be used.

(36) To the photochromic polyurethane composition of the present invention, a novel casting-lamination process has been developed by the inventors. The process essentially comprises: a) preparing a solvent casting solution by dissolving a solid thermoplastic polyurethane, at least one isocyanate polyurethane prepolymer, at least one photochromic compound, and optional stabilizers in a proper solvent; b) cast the solution on a release liner film; c) remove the solvent from the cast film to a substantially dry state to form a photochromic polyurethane film; d) transfer-laminate the photochromic polyurethane film between two transparent resin sheets; e) cure the photochromic polyurethane film, thereby forming a photochromic polyurethane laminate.

(37) To cast a photochromic polyurethane film, a thermoplastic polyurethane, an isocyanate prepolymer, selected photochromic compounds and other necessary additives are first dissolved in a suitable solvent or in a mix of solvents to form a cast solution. The solid concentration in such a solution is usually 15% to 50%, by weight, and the solution has a viscosity suitable for coating. For example, suitable viscosity of the cast solution for using a slot die method is within the range from 500 cPs to 5000 cPs. Examples of suitable solvents that may be used to dissolve polyurethanes include cyclohexane, toluene, xylene and ethyl benzene, esters such as ethyl acetate, methyl acetate, isopropyl acetate, n-propyl acetate, isobutyl acetate, n-butyl acetate, isoamyl acetate, methyl propionate and isobutyl propionate, ketones such as acetone, methylethyl ketone, diethyl ketone, methylisobutyl ketone, acetyl acetone and cyclohexyl ketone, ether esters such as cellosolve aetate, diethylglycol diaetate, ethyleneglycol mono n-butylether acetate, propylene glycol and monomethylether acetate, tertiary alcohols such as diacetone alcohol and t-amyl alcohol and tetrahydrofuran. Ethyl acetate, methyl ethyl ketone, cyclohexane, tetrahydrofuran, toluene and combinations thereof are preferable.

(38) The solution is then cast on a release liner by using a method known to those skilled in the art, such as slot-die, knife-over-roll, reverse-roll, gravure, etc. Slot die and knife-over-film are referred. Slot die method is especially preferred due to its capability to handle wide range of solution viscosity and to cast uniform films. A release liner may consist of a base film and a release coating or simply a film itself. Films with surface energy low enough to provide easy release of the cast film can be used by itself. Examples include low energy polyolefins and fluoropolymers. Most commercially available release liners are based on polyester film coated with a release coating. The release coating has a proper surface energy so that a cast solution or coating forms a uniform film (e.g., without beading) on it. At the same time the release coating does not provide good adhesion to the dried film so that the film can be easily peeled off. Release coatings include silicone (siloxane) based and non-silicone base such as fluoropolymers. A liner based on polyester (PET) with cured siloxane release coating is preferred due to the dimensional stability, flatness, handling, solvent resistance, low cost. Suitable liners should have a thickness of from 25 micrometers to 130 micrometers.

(39) The wet photochromic polyurethane film cast on the release liner is sequentially dried in a forced air oven system. The solvent will be substantially evaporated so that the solvent retention in the photochromic polyurethane film is low enough to not cause any defects (e.g., bubbling) in the future laminate. The solvent retention preferably is less than 2 wt. %, more preferably less than 1 wt. %, and most preferably less than 0.5 wt. %. Conventional methods such as hot air dryers may be used to evaporate the solvent before lamination. The drying conditions, such as temperature and air flow rate in the oven, for a desired solvent retention value depends on the nature of the solvent, the thickness of the cast film, the type of the release liner, and the web speed. The drying conditions should not be so aggressive to cause any surface defects in the cast film. Example defects are blisters (bubbles) and orange peel. Preferably, the drying oven system has multi-zones whose drying conditions are controlled separately.

(40) The thickness of the dried photochromic polyurethane layer is from about 5 micrometers to about 150 micrometers. For using the photochromic laminate in an insert injection molding process to make plastic photochromic lenses, the thickness of the photochromic polyurethane is preferably between 5 micrometers and 80 micrometers. The thickness variation of the photochromic polyurethane layer should be controlled in order to produce a uniform light blockage at the activated state. A thickness variation of less than 15% over the width of the laminate is required and preferably less than 10% and more preferably less than 5%.

(41) The transfer-lamination of the dried photochromic polyurethane film to two transparent resin sheets to form a laminate of the polyurethane film between the two resin sheets, may be done by either a sequential lamination process or an in-line lamination process. In a sequential lamination process, the dried polyurethane film on the release liner is first laminated to the first transparent resin sheet through a first lamination station. The semi-laminate consisting of the release liner, the polyurethane film, and the resin sheet, is then wound up on a core. The wind is then brought to a second lamination station where the release liner is peeled off and the second transparent sheet is laminated to the polyurethane film to form the final photochromic polyurethane laminate. The first and the second lamination stations may be the same one. The lamination may be conducted between two chrome coated steel rolls or between one steel roll and one rubber roll, although the later is preferred.

(42) According to the findings of the inventors, an in-line lamination process is more preferred. In such a process, the second transparent resin sheet is immediately laminated to the semi-laminate without first winding the semi-laminate. The in-line lamination may be done with two two-roll lamination stations, or more conveniently be conducted on one three-roll setup in which the first roll and the second roll form a first nip, and the second roll and the third roll form a second nip. The dried polyurethane film on the release liner is first laminated to the first transparent resin sheet through the first nip. Without forming and winding a semi-laminate, the release liner is peeled off, and the second transparent resin sheet is immediately laminated to the exposed side of the polyurethane film on the first transparent resin sheet, through the second nip. This in-line lamination process will significantly increase the productivity. It also eliminates an extra winding step and reduces the possibilities of defects in the polyurethane film associated with the winding step. Example defects are de-lamination between the polyurethane film and the transparent resin sheet, impressions in the polyurethane film caused by possible external particles under winding pressure.

(43) The photochromic polyurethane laminate thus formed according to the present invention needs to be cured before application. The curing is preferably carried in two stages: a) ambient curing for 1 day to 1 week, b) post curing at elevated temperature of from 50° C. to 130° C. for 8 hours to 1 week.

(44) If the solvent selected to dissolve the photochromic polyurethane composition does not whiten the transparent resin sheet, a direct cast on the resin sheet may be employed. In this case, a simple two-roll lamination setup is acceptable for making a photochromic polyurethane laminate.

(45) In an alternative process, the photochromic layer from a thermoplastic polyurethane and isocyanate-terminated polyurethane prepolymer may be co-extruded utilizing a single- or twin-screw extruder. The extruded photochromic polyurethane film will then be immediately hot-laminated between two transparent resin sheets to form the photochromic polyurethane laminate. The photochromic compounds and other additives may be incorporated into the polyurethane during the resin synthesis stage or melt-mixed prior to extrusion.

(46) Although the photochromic laminate according to the present invention is especially suitable for making photochromic polycarbonate lenses through the insert injection molding process described in commonly assigned U.S. Pat. No. 6,328,446, it can also be used as-is for other photochromic transparencies such as goggles and face shields. The photochromic laminate may also be incorporated into other types of eyewear lenses such as cast resin lenses with a process described in U.S. Pat. No. 5,286,419.

(47) The photochromic polyurethane laminate in accordance with the present invention will now be illustrated with reference to the following examples, which are not to be construed as a limitation upon the scope of the invention in any way.

(48) In the examples, all values are expressions of weight %. CR49 and CR59 are tradenames of photochromic dyes available from Corning Corp. Grey-762 is proprietary grey photochromic dye. Irganox-1010 as an antioxidant, Tinuvin-144 and Tinuvin-765 as light stabilizers are available from CIBA (Tarrytown, N.Y., US).

(49) To visually evaluate the activation and the photochromic polyurethane layer uniformity, a photochromic laminate or lens was exposed to UV irradiation (12 mw/m2) for 5 minutes.

Example 1

(50) Preparation of Isocyanate Polyurethane Prepolymer A: In a 3-necked flask equipped with an overhead stirrer, thermocouple, and a vacuum adapter, 393.5 g (3 equivalents) of 4,4′-dicyclohexylmethanediisocyanate (H12MDI, available from Bayer as Desmodur W) was charged into the reactor and stirred at ambient temperature. 1000 g (2 equivalents) of a polycaprolactone diol having an OH number of 112 mg KOH/g and a number average molecular weight of about 1000 g/mole (available from Dow Chemical as Tone™ 2221) was preheated in an oven to 80° C. and added to the reactor. The mixture was allowed to stir for about 15 minutes, before adding 6 g of dibutyltin dilaurate catalyst (available from Air Products as T-12). The reaction flask was evacuated (<0.1 mm HG) and held at 90° C. for 6 hours. An aliquot of the prepolymer was withdrawn and titrated for isocyanate content using standard n-butyl amine titration. The isocyanate content was found to be 2.92% (theory; 3.0%).

Example 2

(51) Preparation of Isocyanate Polyurethane Prepolymer B: In a 3-necked flask equipped with an overhead stirrer, thermocouple, and a vacuum adapter, 613.0 g (4.67 equivalents) of 4,4′-dicyclohexylmethanediisocyanate (H12MDI, available from Bayer as Desmodur W) was charged into the reactor and stirred at ambient temperature. 1000 g (2 equivalents) of a polycaprolactone diol having an OH number of 112 mg KOH/g and a number average molecular weight of about 1000 g/mole (available from Dow Chemical as Tone™ 2221) was preheated in an oven to 80° C. and added to the reactor. The mixture was allowed to stir for about 15 minutes, before adding 8 g of dibutyltin dilaurate catalyst (available from Air Products as T-12). The reaction flask was evacuated (<0.1 mm HG) and held at 90° C. for 6 hours. An aliquot of the prepolymer was withdrawn and titrated for isocyanate content using standard n-butyl amine titration. The isocyanate content was found to be 6.75% (theory; 7.0%).

(52) Preparation of Thermoplastic Polyurethane: A thermoplastic polyurethane having a theoretical NCO index of 95 was prepared as following. The isocyanate prepolymer B (927.2 g) prepared in Example 2 was heated in vacuo (<0.1 mm HG) with stirring to 80° C. and 1,4-butane-diol (72.8 g) as the chain extender and 3 g of dibutyltin dilaurate catalyst were combined with the prepolymer while keeping stirring. The mixture was stirred for 30 seconds and subsequently poured into a Teflon lined tray. The tray containing the casting was cured in an oven at 85° C. for 24 hours.

Example 4

(53) A solution was first made by dissolving 4 g of the thermoplastic polyurethane prepared in Example 3 in 16 g of anhydrous tetrahydrofuran. To the solution was further added 4 g of the isocyanate prepolymer prepared in Example 1, 0.14 g of CR49 dye, 0.02 g CR59 dye, 0.17 g each of Irganox-1010, Tinuvin-144, and Tinuvin-765. The mixture was stirred at room temperature for 3 hours before cast on an easy release liner (available from CPFilms as T-50) with draw bar targeting a 38 micrometer dry film thickness. The solvent in the cast film was evaporated at 60° C. for 5 minutes with airflow above the film. The dried film was transfer-laminated between two 0.3 mm thick polycarbonate sheets (available from Teijin as PC-1151) with a bench top roller laminator. After 4 days under ambient, the laminate was cured at 70° C. for 3 days.

(54) The laminate was cut into a 76 mm disc and used to make a segmented multi-focal polycarbonate photochromic lens. After the insert injection molding process with common molding parameters, the finished lens had an acceptable thin, crisp segment line. No polyurethane bleeding from the laminate was observed. The lens showed quick and uniform photochromic activation. No any lamination defects were observed.

Example 5

(55) A solution having 28.2% solid, was first prepared by dissolving 1950 g of the thermoplastic polyurethane prepared as in Example 3 in 7550 g of anhydrous tetrahydrofuran. To the solution was further added 780 g of the isocyanate prepolymer prepared as in Example 1, 59 g each of “762” dye, Irganox-1010, Tinuvin-144, and Tinuvin-765. The mixture was stirred at room temperature for 3 hours then set overnight before cast on an easy release liner (available from Saint-Gobain as 8310) at a web speed of 5.5 feet per minute in a pilot coater equipped with a slot die, a two-zone drying oven, and a three-roll lamination station. The solvent in the cast film was evaporated at 70° C. for 1 minute and 120° C. for another minute with forced airflow above the film. The dried film was 38 micrometer thick and had a solvent retention of 0.1%. It was transfer-laminated between two 0.3 mm thick polycarbonate sheets (available from Teijin as PC-1151) with an in-line process (without winding the semi-laminate of the release liner, polyurethane film, and the first polycarbonate sheet). After 4 days in ambient (22° C. and 35%˜50% RH), the laminate was cured at 70° C. for 3 days.

(56) The laminate was cut into 76 mm discs and used to make a segmented multi-focal polycarbonate photochromic lenses. After the insert injection molding process with common molding parameters, the finished lens had an acceptable thin, crisp segment line. No polyurethane bleeding from the laminate was observed. The lens showed quick and uniform photochromic activation. No any lamination defects were observed.

Example 6

(57) A solution having 35.3% solid, was first prepared by dissolving 1950 g of the thermoplastic polyurethane prepared as in Example 3 in 7742 g of anhydrous tetrahydrofuran. To the solution was further added 1950 g of the isocyanate prepolymer prepared as in Example 1, 68 g of CR49 dye, 10 g CR59 dye, 85 g each of Irganox-1010, Tinuvin-144, and Tinuvin-765. The mixture was stirred at room temperature for 3 hours then set overnight, then cast directly on a first 0.3 mm thick polycarbonate sheet (available from Teijin as PC1151) at a web speed of 5.5 feet per minute in a pilot coater equipped with a slot die, a two-zone drying oven, and a three-roll lamination station. The solvent in the cast film was evaporated at 94° C. for 1 minute and 127° C. for another minute with forced airflow above the film. The dried film was 25 micrometer thick and had a solvent retention of 0.1%. A second 0.3 mm thick polycarbonate sheet was laminated on the exposed side of the dried polyurethane film on the first polycarbonate sheet. After 4 days in ambient (22° C. and 35% 50% RH), the laminate was cured at 70° C. for 3 days. The laminate obtained was clear. No solvent whitening on the polycarbonate sheets was seen.

Comparison Example 1

(58) To 10 g of Hysol® (Loctite) U-10FL urethane adhesive resin are dissolved 1.5% of “762” dye, 2.0% of Tinuvin 144, and 2.0% of Tinuvin 765. Then, 9.1 g of Hysol® U-10FL urethane adhesive hardener is mixed in to form a liquid adhesive.

(59) The adhesive was coated with a draw bar directly on a polycarbonate sheet (0.3 mm thick, available from Teijin as 1151) to form a 38 micrometer cast film. Another polycarbonate sheet was laminated onto the adhesive through a bench top roller laminator. Some adhesive was squeezed out. The laminate was allowed to cure at room temperature overnight, then is post cured at 65° C. for 10 hours.

(60) When the photochromic laminate was activated, thin spots (lightly activated due to thinner spots in the polyurethane layer) and non-uniformity of activation due to thickness gradient across the laminate were observed.

Comparison Example 2

(61) Example 4 was followed, except the isocyanate prepolymer was neglected. The photochromic polyurethane layer was 38 micrometers thick. The laminate showed uniform photochromic activation. No lamination defects were observed. However, when molded into a polycarbonate lens as in Example 4, severe polyurethane bleeding was observed at the edge of the laminate.

(62) The foregoing detailed description of the preferred embodiments of the invention has been provided for the purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise embodiments disclosed. Many modifications and variations will be apparent to practitioners skilled in the art to which this invention pertains. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, thereby enabling others skilled in the art to understand the invention for various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the following claims and their equivalents.